Cardiopulmonary Function in Very Preterm Lambs during Liquid Ventilation

Abstract

SummaryCardiopulmonary function was evaluated in very preterm lambs (106 + 0.7 S.E. days gestation, 1.66 -+ 0.12 S.E. kg birth weight) during fluorocarbon ventilation. Lambs were delivered by cesarean section after epidural anesthesia. Indwelling arterial, venous, and tracheal cannulae were placed before clamping the cord. Lambs were then mechanically ventilated with oxygenated fluorocarbon for approximately 2 h. During this period it was possible to maintain adequate gas exchange and stable cardiac function. Transpulmonary pressure, liquid flow, and tidal volume tracings enabled determination of lung compliance, CL = 0.58 + 0.12 S.E. ml*cmHzO-' kg-', inspiratory resistance, RI = 3600 + 604 S.E. ~mHZO*liter-~*sec-', and expiratory resistance, RE = 4034 + 2183 S.E. cmH20/liter/sec. Lung compliance of the 106-day-old fluorocarbon-filled lung is similar to the more mature 138-143-day-old air-filled lung in preterm lambs. Based on the data presented herein we have extended the viability of the preterm lamb to the limit of pulmonary capillary development rather than that of the pulmonary surfactant system. AbbreviationsA-a DO2, alveolar-arterial oxygen gradient CL, lung compliance FRC, functional residual capacity RE, expiratory resistance RI, inspiratory resistance VT, tidal volumeThe lamb has been employed extensively for studying cardiopulmonary development in the perinatal period (1,2,3,12,18,21). But there are few data in very preterm .animals because cardiopulmonary stability and viability are highly correlated with maturity. The majority of studies are those in lamb fetuses at various stages of development (14), exteriorized lambs when the ewe was anesthetized (l,5), or in older lambs delivered by cesarean section after 125 days of gestation (12,18,19,21). Although adequate oxygen transport has been demonstrated by 110 days of gestation in exteriorized preterm fetal lambs, viability of these animals is much later (approximately 140 days, term 145-147 days).Recent studies have revealed the feasibility of ventilation with fluorocarbon liquid in preterm lambs delivered by cesarean section between 135-138 days gestation (17). In contrast to the respiratory problems that occur during mechanical gas ventilation (18, 19, 2 l), lambs ventilated with fluorocarbon liquid exhibited good gas exchange and stable blood gas tensions. It has been suggested that the elimination of high surface forces in the liquid-filled lung could account for improved gas exchange and respiratory stability. The first objective of this study was to quantitate baseline cardiovascular, gas exchange, acid-base balance, and lung mechanics data in very immature lambs using liquid ventilation techniques. There are also apparent differences in lung mechanics between the gas and liquid-filled lungs. With this in mind, we sought to correlate these changes with the differences in physical properties of the respiratory medium. MATERIALS AND METHODS Animalpreparation.Five preterm lambs of 106 -t 0.7 S.E. days gestation (70% of term gestation) and a mean b...

Structural Changes in the Tracheae of Preterm Lambs Induced by Ventilation

“…DISCUSSION These experiments used tracheae from preterm lambs ranging in age from 107 to 116 d of gestation, appropriately oxygenated and ventilated in vivo with liquid fluorocarbon. Cardiopulmonary stability of these preterm lambs with respect to oxygenation, C 0 2 elimination, acid-base, and hemodynamic status was achieved using liquid ventilation support, as this is the only means available currently to ventilate these very premature lambs (15,19). It is important to emphasize the necessity of achieving gas exchange/acid base status within physiologic limits as inability to do so could lead to histochemical damage of the airways, in turn affecting airway structure and function.…”

In Vivo Mechanical Properties of the Developing Airway

“…Recent advances in liquid ventilation techniques have enabled us to establish a stable and viable preterm animal preparation to study physiologic development beginning at the early stages of gestation (15). Using this technology, we evaluated airway compliance and the relaxation time constant of in vivo tracheal segments in lambs to characterize age-related changes in elastic and viscoelastic properties of the developing airway.…”

Liquid Ventilation: From Experimental Use to Clinical Application

“…It has been shown in animals with mature [10,11] and immature [12,13] lungs as well as lungs injured by tracheal instillation of meconium [14] or repeated lung lavage [15], that gas exchange is better in animals man- aged with LV than in those kept on conventional mechanical ventilation (CMV). Gas exchange seems to be independent of endogenous surfactant [16,17], but higher inspiratory pressures are needed to administer the same V T of PFC in animals without surfactant [17,18].…”

“…In adult animals, TLV presents some problems related to a decreased cardiac output and an increase in pulmonary vascular resistance [19]. In immature animals, this does not occur [10,13], since the surface tension is lower than that present in alveoli without surfactant (60 mN/m). This explains the great improvement of gas exchange and C L observed in immature animals.…”